CN103608611B - Twisted spur gear and power transmission - Google Patents

Abstract

The invention provides a helical gear and a power transmission device. The outer peripheral side (24b) has a first side area (24b1), and the first side area (24b1) is set to: from the ring gear portion (22c) near the sleeve portion (22a) side to the outer peripheral side (24b) . Among the distances in the radial direction of the rotating shaft, the distance (W2) at the front end side of the helical gear (21) in the rotation direction (R1) is greater than the distance (W1) at the rear end side.

Description

Helical gears and power transmission devices

technical field

The invention relates to a helical gear and a power transmission device.

Background technique

The schematic structure of the helical gear 21Z is shown in FIG.12 and FIG.13. In addition, FIG. 12 and FIG. 13 show the state in which the gears are tilted (tilted) at the meshing portion of the gears. In addition, the degree of inclination is shown exaggeratedly for easy understanding.

This helical gear 21Z includes: a boss portion 22a mounted on the rotating shaft; a disk portion 22b extending from the boss portion 22a radially outward of the rotating shaft; and a ring gear (rim) provided outside the disk portion 22b. The ring gear portion 22c is provided with teeth 22d inclined with respect to the rotation direction (R) of the gear 21Z on the outer peripheral surface of the ring gear portion 22c.

With such a helical gear 21Z, the teeth are inclined with respect to the direction of rotation of the gear. As a result, the tooth contact torque is dispersed in a direction intersecting the rotational direction of the gear (thrust direction (direction S in FIG. 13 )), so that noise can be suppressed and torque fluctuations are small. However, when the torque is dispersed, as shown in FIG. 13 , the helical gear 21Z tilts in the thrust direction (S direction), thereby increasing vibration and noise, and sufficient suppression of vibration and noise cannot be expected.

Gears disclosed in JP 2009-228741, JP 2010-101334, JP 2008-303968, JP 2005-325865, and JP 2005-069401 Among them, a through hole is provided in the plate of the gear, and the vibration and noise are suppressed by studying the rigidity of the plate.

Patent Document 1: Japanese Patent Laid-Open No. 2009-228741

Patent Document 2: Japanese Patent Laid-Open No. 2010-101334

Patent Document 3: Japanese Patent Laid-Open No. 2008-303968

Patent Document 4: Japanese Patent Laid-Open No. 2005-325865

Patent Document 5: Japanese Patent Laid-Open No. 2005-069401

The schematic structure of the helical gear 21Y is shown in FIG.14 and FIG.15. In addition, FIG. 14 and FIG. 15 show the state in which the gears are tilted (tilted) at the meshing portion of the gears. In addition, the degree of inclination is shown exaggeratedly for easy understanding.

In this helical gear 21Y, a plurality of through-holes H21 extending in the circumferential direction around the rotation axis are provided in the disk portion 22b. Thereby, by changing the rigidity along the circumferential direction of the disk portion 22b located between the boss portion 22a and the ring gear portion 22c, as shown in FIG. 15 , the helical gear 21Z can be largely tilted in the thrust direction. Thereby, the increase of vibration and noise can be suppressed.

However, when the sleeve portion 22a is viewed from the ring gear portion 22c, in the radial direction of the rotating shaft, the rigidity of the disk portion 22b in the area where the through hole H21 is not provided is not as rigid as that of the disk portion 22b in the area where the through hole H21 is provided. sharp change in rigidity.

Therefore, in the through hole H21, the stress generated in the disk portion 22b is extremely extreme on the head side in the rotation direction of the helical gear 21Y (the front end side (in the rotation direction R1) (the region surrounded by A1 in FIG. 14 )). increase, there is a possibility that the strength of the ring gear portion 22c on the side of the meshing development direction of the through hole H21 is insufficient. On the other hand, in order to eliminate this lack of strength, for example, when the thickness of the disk portion 22b is increased, the rigidity is increased, and vibration and noise may increase.

Contents of the invention

The present invention has been made in view of the above problems, and an object of the present invention is to provide a helical gear and a power transmission device that can suppress vibrations and noises, and can generate vibrations on the front end side of the rotation direction of the through-hole provided in the disc portion. Stress-reducing construction.

The helical gear according to the present invention includes: a boss portion fitted to the rotating shaft; a disk portion extending radially outward from the boss portion toward the rotating shaft; and a ring gear portion. A portion is disposed outside the disk portion, the ring gear portion includes a plurality of teeth on its peripheral surface, and the disk portion includes a plurality of opening peripheral walls defining through holes provided along the circumference of the sleeve portion.

The opening peripheral wall includes: an inner peripheral side, the inner peripheral side is located on the sleeve portion side; an outer peripheral side, the outer peripheral side is located closer to the ring gear than the inner peripheral side; a first end side, the a first end side connecting one end of the inner peripheral side and one end of the outer peripheral side; and a second end side connecting the other end of the inner peripheral side and the other end of the outer peripheral side.

The outer peripheral side surface has: a first side area; and a second side area, the second side area is located closer to the rear end side of the helical gear in the rotation direction than the first side area, and the first side area is provided to : The position located on the frontmost side in the direction of rotation of the helical gear in the distance from the position of the ring gear part on the side of the boss part to the outer peripheral surface in the radial direction of the rotation shaft distance max.

In another form, the first side area and the second side area are continuously provided via a connecting portion, and the first side area and the second side area are provided such that the first side area and the second side area are separated by the The connecting portion is left-right symmetrical.

In another manner, the above-mentioned first side area is configured in a curved shape.

In another form, the above-mentioned first side area is arranged in a linear shape.

A power transmission device according to the present invention includes the helical gear described above.

According to the helical gear and the power transmission device according to the present invention, there is provided a helical gear and a power transmission device capable of suppressing vibration and noise, and capable of reducing the stress generated on the front end side in the rotation direction of the through-hole provided in the disc portion. structure.

Description of drawings

1 is a cross-sectional view showing the configuration of a transaxle (power transmission device) in which a transmission including a helical gear according to the present embodiment is integrated with a transaxle.

FIG. 2 is a schematic diagram illustrating a meshing state of a gear device having a three-shaft structure including helical gears according to the present embodiment.

FIG. 3 is a front view showing the helical gear of this embodiment.

Fig. 4 is a partially enlarged plan view of the helical gear of the present embodiment.

Fig. 5 is a cross-sectional view showing deformation when the helical gears mesh, viewed from the arrow direction along the line V-V in Fig. 3 .

Fig. 6 is a front view showing a helical gear of the background art.

Fig. 7 is a cross-sectional view taken along line VII-VII of Fig. 6 viewed from the direction of the arrow.

FIG. 8 is a graph showing the relationship between the stress of the helical gear and the phase of the through-hole in the present embodiment.

FIG. 9 is a graph showing the relationship between the stress of the helical gear of the background art and the phase of the through-hole.

Fig. 10 is a front view showing a helical gear according to another embodiment.

Fig. 11 is a front view showing a helical gear according to yet another embodiment.

FIG. 12 is a front view showing deformation of helical gears in the background art when meshing.

Fig. 13 is a sectional view taken along line XIII-XIII in Fig. 12 viewed from the direction of the arrow.

Fig. 14 is a front view showing deformation during meshing of another helical gear of the background art.

Fig. 15 is a cross-sectional view taken along line XV-XV in Fig. 14 viewed from the direction of the arrow.

detailed description

Embodiments of the present invention will be described below based on the drawings. In addition, in the following drawings, the same reference numerals are attached to the same or corresponding parts, and descriptions thereof will not be repeated.

In addition, in the embodiments described below, the various constituent elements are not essential to the present invention unless otherwise described. In addition, in the following embodiments, when referring to the number, amount, etc., unless otherwise specified, the above-mentioned number, etc. are only examples, and the scope of the present invention is not necessarily limited to the number, amount, etc. .

1 is a cross-sectional view showing a configuration of a transaxle in which a transmission including a gear unit using a helical gear according to the present embodiment and a transaxle are integrated. The transmission shown in FIG. 1 is a transmission used in a front-wheel drive hybrid vehicle.

As shown in FIG. 1 , the transaxle includes rotating electric machines 100 and 200 ; planetary gears 300 for power distribution; and a differential mechanism 400 . The rotary electric machines 100, 200, the planetary gear 300, and the differential mechanism 400 are disposed in the casing.

The rotary electric machine 100 includes a rotary shaft 10 as a first shaft, and the rotary shaft 10 is provided rotatably with respect to a housing. The rotary electric machine 200 includes a rotary shaft 20 as a second shaft, and the rotary shaft 20 is provided so as to be rotatable with respect to the housing. The rotating electric machines 100 and 200 include: a stator core formed by laminating electromagnetic steel sheets; and a stator coil wound around the stator core. The terminals of the stator coils are connected to the power supply cables from the external power supply, and the external power supply is electrically connected to the stator coils.

The planetary gears 300 are connected to the rotary shaft 20 . The planetary gear 300 distributes and transmits the engine power transmitted through the rotary shaft 20 to the rotary shaft 10 and the rotary shaft 30 as a third shaft.

The differential mechanism 400 includes a final driven gear 91 . The final driven gear 91 is connected to the rotary shaft 30 via the final drive gear 81 . The differential portion 90 receiving power transmission from the rotary shaft 30 transmits equal driving force to both wheels while changing the rotational speed of the left and right wheels when the vehicle turns.

In this way, the transaxle shown in FIG. 1 functions as a power transmission device that transmits the rotational driving force input from the crankshaft of the electric motor and the engine and outputs it to drive wheels.

In this transaxle, in order to achieve size reduction, weight reduction, and cost reduction, a three-shaft gear unit in which one gear has two meshing portions is used as a transmission for outputting electric motor power and engine power.

A first gear 11 is provided on the rotating shaft 10 . A second gear 21 is provided on the rotating shaft 20 . A third gear 31 is provided on the rotating shaft 30 . Helical gears are used for the first gear 11, the second gear 21, and the third gear 31, respectively.

Referring to FIG. 2, the meshing state of the gear mechanism of the three-shaft structure is shown. As shown in FIG. 2 , the first gear 11 meshes with the second gear 21 at the meshing point 41 . The second gear 21 meshes with the third gear 31 at the meshing point 42 . The power transmission device includes a gear unit including a first gear 11 , a second gear 21 , and a third gear 31 . The meshing point 41 is the meshing position of the first gear 11 and the second gear 21 . The meshing point 42 is a meshing position of the second gear 21 and the third gear 31 .

Here, the detailed structure of the helical gear 21 as the second gear will be described with reference to FIGS. 3 to 5 . In addition, FIG. 3 is a front view showing the helical gear 21 of this embodiment, FIG. 4 is a partially enlarged plan view of the helical gear 21 of this embodiment, and FIG. The figure in FIG. 1 corresponds to a cross-sectional view of deformation of the helical gear 21 during meshing. In addition, the same helical gears as in the present embodiment may be used for the helical gears used for the first gear 11 and the third gear 31 .

The helical gear 21 includes: a boss portion 22a fitted to the rotating shaft 20; a disk portion 22b extending radially outward from the boss portion 22a toward the rotating shaft 20; and a ring gear portion 22c. The ring gear portion is provided outside the disk portion 22b. The ring gear portion 22c includes a plurality of teeth 22d on its outer peripheral surface.

The disk portion 22b includes an opening peripheral wall 24 defining a through-hole H11 provided along the circumference of the boss portion 22a. In this embodiment, the opening peripheral wall 24 is provided in three places at a pitch of 120°.

The opening peripheral wall 24 of this embodiment includes: an inner peripheral side 24a, which is located closer to the sleeve portion 22a; an outer peripheral side 24b, which is located closer to the ring gear 22c than the inner peripheral side 24a; One end side 24c, the first end side connects one end of the inner peripheral side 24a and one end of the outer peripheral side 24b; and the second end side 24d, the second end side connects the other end of the inner peripheral side 24a and the outer periphery The other end of side 24b.

The inner peripheral side surface 24a is constituted by a part of an arc whose center is the rotation center (also the center of the boss portion 22a ) C1 of the rotation shaft 20 and whose radius is D1. Moreover, the 1st end side surface 24c and the 2nd end side surface 24d are comprised by the semicircle centering on rotation center C2, and having a radius D2.

The outer peripheral side surface 24b has a first side surface area 24b1 provided such that the distance from the ring gear portion 22c on the sleeve portion 22a side to the outer peripheral side surface 24b in the radial direction of the rotating shaft , the distance W2 at the frontmost side of the rotation direction (R1) of the helical gear 21 (the side closest to the line (1) in the area surrounded by A1 in the figure) is greater than the distance at the connection part P1 at the rear end side W1. The first side area 24b1 has a curved shape that is convex toward the ring gear portion 22c side.

The outer peripheral side surface 24b of this embodiment has the 2nd side surface area 24b2 located in the rear end side of the rotation direction R1 of the helical gear 21 rather than the 1st side surface area 24b1. The second side area 24b2 is provided continuously with the first side area 24b1 via the connecting portion P1, and the first side area 24b1 and the second side area 24b2 are provided such that the first side area 24b1 and the second side area 24b2 are separated by the connecting portion P1. It is left-right symmetrical. Therefore, the through hole H11 defined by the opening peripheral wall 24 is formed to be left-right symmetrical with respect to the virtual straight line L1 connecting the rotation center C1 and the connection part P1.

Here, the shape of the helical gear 21Y of the background art will be described with reference to FIGS. 6 and 7 . In addition, FIG. 6 is a front view showing a helical gear 21Y of the background art, and FIG. 7 is a cross-sectional view showing deformation of the helical gear 21Y when meshing corresponding to a diagram viewed from the arrow direction along line VII-VII of FIG. 6 . .

The helical gear 21 of this embodiment shown in FIG. 3 has the same basic shape as the helical gear 21Y of the background art, but the shape of the opening peripheral wall 25 defining the through hole H21 provided in the disk portion 22b is different.

In the helical gear 21Y, the opening peripheral wall 25 includes: an inner peripheral side surface 25a located closer to the hub portion 22a side; and an outer peripheral side surface 25b located closer to the ring gear portion 22c side than the inner peripheral side surface 25a. position; the first end side 25c, which connects one end of the inner peripheral side 25a and one end of the outer peripheral side 25b; and the second end side 25d, which connects the other end of the inner peripheral side 25a One end and the other end of the peripheral side 25b.

The inner peripheral side surface 25a is constituted by a part of an arc whose center is the rotation center C1 of the rotation shaft 20 and whose radius is D11. The outer peripheral side surface 25b is constituted by a part of an arc whose center is the rotation center C1 of the rotation shaft 20 and whose radius is D12 (D12>D11). And the 1st end side surface 25c and the 2nd end side surface 25d are comprised by the semicircle centering on the said rotation center C2, and having a radius D2.

The outer peripheral side surface 25b is provided so that the outer peripheral side surface 25b may be left-right symmetrical across the connecting portion P1. Therefore, the through-hole H21 defined by the opening peripheral wall 25 is formed to be left-right symmetrical with respect to the virtual straight line L1 connecting the rotation center C1 and the connection part P1.

The outer peripheral side surface 25b is constituted by a part of an arc whose center is the rotation center C1 of the rotation shaft 20 and whose radius is D12. Therefore, it is positioned at the foremost end in the rotation direction R1 of the helical gear 21Y in the distance in the radial direction of the rotation shaft. The distance W2 at the position on the side (the side closest to the line (1) in the area surrounded by A1 in the figure) is the largest.

Using FIG. 5 and FIG. 7 to compare the deformation of the helical gear 21 of the present embodiment having the structure shown in FIG. 3 and the helical gear 21Y of the background art shown in FIG. The inclination angle α1 of the helical gear of this embodiment is smaller than the inclination angle α2 of the helical gear 21Y shown in FIG. 6 .

On the other hand, the inclination angle α1 of the helical gear 21 of this embodiment is larger than the inclination angle α3 of the helical gear 21Z shown in FIG. That is, the following relationship is established: tilt angle α2 of the helical gear 21Y>tilt angle α1 of the helical gear 21>tilt angle α3 of the helical gear 21Z.

8 shows the relationship between the through-hole phase and stress of the helical gear 21 according to the present embodiment, and FIG. 9 shows the relationship between the through-hole phase and stress of the helical gear 21Y of the background art. (1) in each figure shows the position on the frontmost side in the rotation direction R1 of the helical gear 21 among the positions of the through holes shown in FIG. 3 and FIG. 6 . In FIG. 8 and FIG. 9 , the tooth width end LH means the position of the tooth located on the left side (rear side in the figure) when viewed in the direction of rotation, and the center of the tooth width means the position of the tooth located in the center when viewed in the direction of rotation. The position of the tooth width end RH means the position of the tooth located on the right side (near side in the figure) as viewed in the direction of rotation.

As shown in FIG. 9 , the phase stress of the through hole of the helical gear 21Y of the background art occurs at a position on the front end side in the rotation direction R1 of the helical gear 21 (the position of the through hole indicated by (1)). Stress over 700Mpa.

This is because, when the gear meshes at a portion where the difference in rigidity between the through hole and the disc portion is large, large deformation occurs in the helical gear. As a result, the meshing teeth are pushed and deformed by the rigid parts. As a result, the engaged dedendum is stretched resulting in higher stress at the dedendum. Therefore, in a gear having a through hole in the disc portion, it is considered that the dedendum strength becomes extremely disadvantageous, and a large stress is generated.

On the other hand, regarding the stress of the through-hole phase of the helical gear 21 in this embodiment, there is a possibility that the stress may be increased at the position on the front end side in the rotation direction R1 of the helical gear 21 (the position of the through-hole shown by (1)). Reduced to a stress not exceeding 700Mpa.

This is because the curvature of the first side area 24b1 is changed from the rotation center C2 when the through hole is viewed along the rotation direction, and the first side area 24b1 is provided so as to extend from the hub portion 22a of the ring gear portion 22c. Among the distances in the radial direction of the rotating shaft from the position on the side to the outer peripheral side surface 24b, the distance W2 at the position on the frontmost side in the rotation direction R1 of the helical gear 21 is the largest.

Accordingly, when the through hole H11 is viewed along the rotation direction, the thickness of the disk portion 22b becomes gradually thinner, so that the difference in rigidity of the disk portion 22b can be made from the end portion of the through hole H11 toward the central portion (connection portion P1). Changes smoothly. As a result, deformation in which the tooth is pressed by the highly rigid portion can be alleviated, and an increase in stress at the dedendum can be suppressed.

In this way, in the helical gear of the present embodiment, while suppressing vibration and noise, it is possible to reduce the stress generated on the front end side in the rotation direction of the through-hole provided in the disk portion. As a result, the performance of the gear unit using the helical gear and the transaxle including the gear unit can be improved.

In addition, in this embodiment, as a shape of the outer peripheral side surface 24b, it is provided so that it may become bilateral symmetry across the connection part P1. This is because the same effect can be obtained even when the rotation direction of the gear is reversed. In addition, the case where the first side region 24b1 and the second side region 24b2 are directly connected at the connecting portion P1 as the outer peripheral side surface 24b has been described, but it may also be sandwiched between the first side region 24b1 and the second side region 24b2. Contains a part of an arc centered on the center of rotation C1.

(Other implementations)

Furthermore, as another embodiment, a helical gear 21A having an opening peripheral wall 25A defining a through hole H12 as shown in FIG. 10 can also be employed. In addition, this helical gear 21A differs from the helical gear 21 shown in FIG. 3 in that the shape of the peripheral wall of the opening is different, so the same or corresponding parts are given the same reference numerals and will not be described again.

The opening peripheral walls 25A are provided at three locations at a pitch of 120°. The opening peripheral wall 25A includes: a first opening peripheral wall 25R located on the front end side in the rotation direction of the helical gear 21A; and a second opening peripheral wall 25L located on the rear end side in the rotation direction of the helical gear 21A . The 1st opening peripheral wall 25R and the 2nd opening peripheral wall 25L are connected by the connection part P1.

The first opening peripheral wall 25R includes: a first inner peripheral side 25a1 located closer to the sleeve portion 22a; A position on the side of the ring gear portion 22c; and a first end side surface 25c1 connecting one end of the first inner peripheral side surface 25a1 and one end of the first outer peripheral side surface 25b1.

The second opening peripheral wall 25L includes: a second inner peripheral side 25a2 located closer to the sleeve portion 22a; a second outer peripheral side 25b2 located closer to the second inner peripheral side 25a2; A position on the side of the ring gear portion 22c; and a second end side surface 25c2 connecting one end of the second inner peripheral side surface 25a2 and one end of the second outer peripheral side surface 25b2.

The second inner peripheral side surface 25a2 is constituted by a part of an arc whose center is the rotation center C1 of the rotation shaft 20 and whose radius is D11. Furthermore, the second outer peripheral side surface 25b2 is constituted by a part of an arc whose center is the rotation center C1 of the rotation shaft 20 and whose radius is D21 (D21>D11).

The first end side surface 25c1 and the second end side surface 25c2 are composed of a semicircle whose center is the rotation center C2 and whose radius is D2.

The first outer peripheral side surface 25b1 is provided so as to be located in the rotational direction R1 of the helical gear 21 in the distance in the radial direction of the rotation shaft from the position on the boss portion 22a side of the ring gear portion 22c to the first outer peripheral side surface 25b1. The distance W2 at the front end side (the side closest to the line (1) in the area surrounded by A1 in the figure) is greater than the distance W1 at the connecting portion P1 on the rear end side. The first outer peripheral side surface 25b1 is linear.

The first inner peripheral side surface 25a1 is provided substantially parallel to the first outer peripheral side surface 25b1, and the first inner peripheral side surface 25a1 is also linear.

In the helical gear 21A, when the rotation direction is R1, the region of the first opening peripheral wall 25R is under the same conditions as the helical gear 21 described above, so the same effect can be obtained.

In addition, for the helical gear 21 shown in FIG. 3 and the helical gear 21A shown in FIG. 10 , the opening peripheral walls are provided at three locations at intervals of 120°, but the number is not limited thereto. For example, as shown in FIG. 11 , it is also possible to employ a helical gear 21B in which the helical gear 21A shown in FIG. 10 is modified and the opening peripheral walls 25A are provided at four places at 90° pitches. The opening peripheral wall 24 of the helical gear 21 can also be provided at four places at a pitch of 90°. In addition, the opening peripheral walls may be provided at a plurality of positions at equal intervals as required.

Embodiments and examples disclosed this time are illustrative in all points and should not be considered as a restrictive description. The scope of the present invention is shown not by the above-described description but by the claims, and it is intended that all changes within the meaning and scope equivalent to the claims are included.

Industrial Utilization Possibility

The present invention is particularly suitable for gear devices such as transmissions and transfer cases of vehicles.

Symbol Description:

10, 20, 30...Rotating shaft; 11...First gear (helical gear); 21...Second gear (helical gear); 22a...Sleeve part; 22b...Disc part; 22c...Ring gear part; 22d...Tooth; 24...opening peripheral wall; 24a...inner peripheral side; 24b...outer peripheral side; 24b1...first side area; 24b2...second side area; 24c...first end side; 24d...second end side; 21A, 21B... Helical gear; 25A...opening peripheral wall; 25L...second opening peripheral wall; 25R...first opening peripheral wall; 25a1...first inner peripheral side; 25a2...second inner peripheral side; 25b1...first outer peripheral side; 25b2...second outer peripheral Side; 25c1...first end side; 25c2...second end side; 31...third gear (helical gear); 41, 42...meshing point; 81...final drive gear; 90...differential part; 91... Final driven gear; 100, 200...rotating motor; 300...planetary gear; 400...differential mechanism; C1...rotation center; H11, H12...through hole; P1...connecting part.

Claims (5)

1. A helical gear, The helical gear (21) includes: a sleeve portion (22a) mounted on a rotating shaft; a disk portion (22b) extending from the sleeve portion (22a) toward the rotating shaft extends radially outward; and a ring gear portion (22c) provided on the outer side of the disc portion (22b), in, The ring gear portion (22c) includes a plurality of teeth (22d) on its outer peripheral surface, The disc portion (22b) includes a plurality of opening peripheral walls (24), and the opening peripheral walls (24) define through holes (H11) arranged along the periphery of the sleeve portion (22a), The opening peripheral wall (24) includes: an inner peripheral side (24a), the inner peripheral side (24a) is located on the side of the sleeve part (22a); an outer peripheral side (24b), the outer peripheral side (24b) being located closer to the ring gear portion (22c) than the inner peripheral side (24a); a first end side (24c) connecting one end of said inner peripheral side (24a) and one end of said outer peripheral side (24b); and a second end side (24d), the second end side (24d) connecting the other end of the inner peripheral side (24a) and the other end of the outer peripheral side (24b), The outer peripheral side (24b) has: a first side area (24b1); and a second side area (24b2), the second side area (24b2) is located closer to the helical gear ( 21) The position of the rear end side in the direction of rotation (R1), The first side surface area (24b1) is provided so as to extend from a position of the ring gear portion (22c) on the sleeve portion (22a) side to the outer peripheral side surface (24b) on the axis of rotation. Among the distances in the radial direction of the helical gear (21), the distance (W2) at the position on the frontmost side in the direction of rotation (R1) of the helical gear (21) is the largest, said first side area (24b1) and said second side area (24b2) are arranged continuously by means of a joint (P1), When the through hole (H11) is viewed along the rotation direction (R1), the thickness of the disk portion (22b) gradually becomes thinner, and the difference in rigidity of the disk portion (22b) increases from the through hole The end portion of (H11) gradually changes toward the connection portion (P1). 2. The helical gear according to claim 1, wherein, The first side area (24b1) and the second side area (24b2) are arranged such that the first side area (24b1) and the second side area (24b2) interpose the connecting portion (P1) It is left-right symmetrical. 3. The helical gear according to claim 1 or 2, wherein, The first side area (24b1) is provided in a curved shape. 4. The helical gear according to claim 1 or 2, wherein, The first side area (24b1) is arranged in a linear shape. 5. A power transmission device wherein, The power transmission device includes the helical gear according to claim 1 .